First: it takes two to create marital problems. No, it doesn't. It only takes one.
It feels embarrassing even to have to say that, it's such a Biblically obvious point — but the notion of necessarily democratically-shared liability is so widespread that some air-clearing is necessary.
I think I'll call this the Democratic Causality Myth. How do I know it's a myth? The same way I know anything really important: the Bible.
For this is a gracious thing, when, mindful of God, one endures sorrows while suffering unjustly. For what credit is it if, when you sin and are beaten for it, you endure? But if when you do good and suffer for it you endure, this is a gracious thing in the sight of God. (1 Peter 2:19-20)There you go: it is possible to suffer, not only in spite of doing good, but precisely for doing good. Peter expressly envisions a relationship where Party A causes suffering to Party B, and the latter not only did not "have it coming to him," but was specifically doing what he ought to be doing.
Peter's not done with that theme. Note that he says in 3:14a, "even if you should suffer for the sake of righteousness, you are blessed." There it is again: suffering precisely because one had done what was right.
Of course, we could add a heap of Scriptures, and they'd take us back to our Lord Himself, amid the Beatitudes: "Blessed are those who are persecuted for righteousness' sake, for theirs is the kingdom of heaven" (Matt. 5:10).
The assumption that all suffering must be immediately traceable to some specifically causative wrongdoing is simply not Biblical. It is to join hands and nod along with Job's divinely-discredited friends, as they doggedly pursue the etiology of Job's suffering, sure that he'd brought it on himself somehow.
So if we grant this for all of life, is there some force-field that un-trues the truth when it comes to marriage? Is it only in marriage that we must always split blame for suffering 50-50? I'd like to see that logic diagrammed.
Now let me hasten to say (if it isn't too late to "hasten") that the odds are that there never has been a troubled marriage involving one 100% flawless saint and one 100% culpable reprobate. And anyone who was trying to help a troubled couple would be a fool to overlook the wisdom of Prov. 18:17. We sinners being what we are (sinners, and rationalizing ones at that), the odds are that both parties in a struggling marriage have sin-patterns to deal with. You, the person in a troubled marriage, should start with that assumption.
But really — a woman's husband commits adultery. You immediately begin to search for what she did to bring this on herself? On what Biblical warrant? Even if you can find twelve things she did wrong as a wife, does that make his sin of adultery to any degree her fault? A man's wife incessantly tongue-lashes and emasculates him. First thing you do is start listing off his failure as a leader? On what Biblical warrant? Even if you can find twelve things he did wrong as a husband, does that make her sin of verbal assaults to any degree his fault?
In case I haven't made this clear, I am writing to you. I am not writing to your spouse. You (and I) need to own your (and my) sin, period, and not race for cover behind the democratic causality myth.